1. Field of the Invention
This invention relates to an electrical heating device with at least one heat generating element with at least one PTC element and with strip conductors contacting on both sides for supplying electrical current to the PTC element and with heat emitting elements which form opposing surfaces for contacting the heat generating element.
2. Description of the Related Art
Electrical heating devices of this nature are generally known and are particularly employed as heating devices in motor vehicles.
For example, EP 2 109 345 A1 can be regarded as class-forming, which discloses an electrical heating device for heating air and with which the heat emitting elements are formed as lamellar layers, which contact the heat generating elements through the intermediate positioning of an insulating film, i.e. which form the opposing surface for abutting the heat generating element. In this state of the art the heat generating element comprises a two-part housing, whereby each housing part encloses one of the two strip conductors. The two housing parts are situated mutually opposite with the intermediate positioning of a compressive sealing means. In this way, through a pressure acting from outside, for example the pressure of a spring which holds a layer structure of a plurality of layers of heat emitting and heat generating elements under tension in a frame, the possibility is created of the strip conductors directly contacting the PTC element so that current is reliably introduced into the PTC element and heat can be coupled out of the PTC element.
In another state of the art, EP 1 931 176 A1, the heat generating element is located in a U-shaped pocket open on one side and is wedged in the pocket with a wedge element. The wedge element contacts the heat generating element through the intermediate positioning of an electrical insulating layer to electrically decouple it from the walls forming the pocket. The walls are normally part of a standardised housing which comprises a heating chamber through which the fluid to be heated can pass. The wedge element introduced into the pocket should in this respect ensure that the strip conductors abut the PTC elements with a good contact. With the previous state of the art the heat generating element comprises a plurality of PTC heating elements provided directly adjacently.
With a further state of the art according to EP 1 574 791 A1 a plurality of heat emitting elements are provided in a frame layered with a plurality of heat generating elements. The heat emitting elements comprise vanes which essentially extend transversely to the layers of the layer structure. The layer structure is held in a frame under spring tension. The heat emitting elements are aluminium extruded sections which directly abut the PTC heating elements. Accordingly, with this previously known state of the art, which can also be regarded as class-forming, the strip conductors are formed, for the purposes of this invention, by the mutually opposing outer surfaces of the heat emitting elements, between which the PTC heating elements are enclosed and electrically supplied.
With a further state of the art given in EP 0 899 985 the PTC heating elements are present between extruded sections which have holes for the passage of the fluid to be heated. The extruded sections are clamped together, enclosing the PTC heating elements in order to achieve as good an electrical contact as possible.
PTC heating elements, which are used in the electrical heating devices mentioned above, are ceramic components that are manufactured by sintering. Normally the oppositely situated surfaces provided for receiving the electrical supply are metallised, for example by means of screen printing. Both the application of the metallisation and the production of the PTC heating elements of this nature can lead to the thickness of the PTC heating elements varying. With a permanently specified alignment of the strip conductors certain differences in thickness already lead to the problem that individual PTC elements, which are arranged adjacently in a plane and between strip conductors, do not sufficiently contact the strip conductors. This can lead to spark formation and thermal disturbances within the electrical heating device which do not just impair the service life of the electrical heating device, but also detrimentally affect a controller assigned to the electrical heating device, in particular when an electronic controller with power switches is involved.